1. Field of the Invention
This invention relates to a punching device, more particular to a punching device including a pair of driving levers for driving a punch to slide against a die for cutting a sheet.
2. Description of the Related Art
Referring to FIG. 1, Taiwanese Patent Application No. 81203592 discloses a conventional punching device 100 that is used in the craft industry for cutting a sheet (not shown), such as a paper sheet and a plastic sheet, in a predetermined pattern to form a craft article. The punching device 100 includes a base 11, a punch 12, a compression spring 13, a pressing button 14, and a cap 15. The base 11 includes a bottom plate 111 and a supporting plate 112 parallel to and connected to the bottom plate 111 and cooperating with the bottom plate 111 to define a gap 10 for extension of the sheet therein. The bottom plate 111 is formed with a die hole 113 for passage of the punch 12 therethrough. The pressing button 14 is seated on the punch 12 for pressing the punch 12 against the compression spring 13 so as to move the punch 12 along a vertical axis (X) into and through the die hole 113 in the bottom plate 111, thereby cutting the sheet. The compression spring 13 restores the punch 12 to its original position after punching. The cap 15 covers the punch 12 and the supporting plate 112 and is formed with a top opening for extension of the pressing button 14 therethrough. Since the force acted on the pressing button 14 is directly transmitted to the punch 12 in the vertical axis (X), it is laborious when using the aforesaid punching device to cut a thick sheet.
Referring to FIG. 2, U.S. Pat. No. RE38219 discloses a punching device 200 including a base 21, a punch 22, a compression spring unit 23, a cap 24 and a pressing lever 25. The base 21 has a bottom plate 211 and a supporting plate 212 disposed above and connected to the bottom plate 211 through a connecting wall 217 and cooperating with the bottom plate 211 to define a gap 213 therebetween for receiving a sheet (not shown) therein. The bottom plate 211 is formed with a die hole 214. The supporting plate 212 has one end provided with a pivot seat 216, and is formed with a through-hole 215 aligned with the die hole 214 for extension of the punch 22 therethrough and into the die hole 214. The punch 22 has a bottom blade edge 221 for cutting the sheet. The compression spring unit 23 abuts against the supporting plate 212 and the punch 22 for restoring the punch 22 to its original position. The pressing lever 25 has a pivot end 251 pivoted to the pivot seat 216, a pressing end 253 opposite to the pivot end 251, and a driving protrusion 252 that is disposed between the pivot end 251 and the pressing end 253 and that is aligned with the punch 22 along a vertical axis (Y) perpendicular to the sheet. When the pressing end 253 of the pressing lever 25 is pressed, the driving protrusion 252 presses the punch 22 to move along the vertical axis (Y) into and through the die hole 214, thereby cutting the sheet.
Although the pressing lever 25 of the punching device 200 permits a less force required to punch the sheet as compared to the previous conventional punching device 100, it undesirably and considerably increases the length of the punching device 200 attributed to the length of the pressing lever 25. Moreover, according to the lever principle, the shorter the distance between the pivot end 251 (fulcrum) and the driving protrusion 252 (load) and the longer the distance between the pivot end 251 and the pressing end 253 (effort), the more will be the mechanical advantage, i.e., the less effort is required. Since the contact between the driving protrusion 252 and the punch 22 is required to be located on the vertical axis (Y) in order to prevent imbalance problem for the punch 22 (inclination of the punch 22 or uneven movement of the punch 22) from occurring, the distance between the pivot end 251 and the driving protrusion 252 is fixed and cannot be reduced. As a consequence, the longer the distance between the pivot end 251 and the driving protrusion 252, the longer the distance between the pivot end 251 and the pressing end 253 is required to maintain the same effort. In addition, since the pressing end 253 of the pressing lever 25 is located at one side of the punch device 200 and is relatively far from the vertical axis (Y), the dimensions of the base 21 are required to be enlarged in order to increase the stability of the punch device 200 and to prevent the punch device 200 from raising up or flipping over upon pressing of the pressing end 253, thereby further increasing the overall size of the punch device 200.